This invention relates to a method of catalytically converting olefins into higher hydrocarbons. This invention more particularly relates to a method for converting ethylene to higher hydrocarbons by contact with siliceous crystalline molecular sieves. Conversion of various hydrocarbon fractions with acidic catalysts generally and more particularly with siliceous crystalline molecular sieves is well known in the art. The conversions for which such catalysts have been used include cracking, isomerization, hydrocracking, etc. Molecular sieves have also been used for the conversion of hydrocarbon feeds consisting essentially of C.sub.2 -C.sub.5 olefins, mixtures thereof, and mixtures thereof with paraffins to higher molecular weight products.
U.S. Pat. No. 3,325,465 teaches a process for polymerizing olefinic hydrocarbons over zeolites, the initially present cations of which have been partially exchanged with cations selected from the group consisting Co,Ni and rare earth cations. Ethylene polymerization at atmospheric pressure is described in Examples 3-8 of the patent. At column 6, lines 41-47, the patent teaches that use of atmospheric pressure is preferred, although pressures up to 1000 atmospheres may be used. Higher pressures are said to increase throughput but increase the risk of catalyst deactivation. Operating temperatures of 25 .degree. to 400 .degree. C. and space velocities of 50 to 1000 hr..sup.-1 VHSV (volume hourly space velocity), preferably less than 300 hr. .sup.-1 VHSV, are taught. Hydrocarbon diluents such as paraffins and/or cycloparaffins may be present in the olefinic feedstock, but the patent does not indicate what effect such presence may have on selection of operating parameters for the process.
U.S. Pat. No. 3,760,024 teaches preparation of aromatic compounds by contacting C.sub.2 -C.sub.4 paraffins and/or olefins with a ZSM-5 type zeolite. Operating temperatures of 100.degree.-700.degree. C., operating pressures of 0-1000 psig (preferably 0-500 psig), and space velocities of 0.5-40 hr. .sup.-1 WHSV (weight hourly space velocity) are taught. The particular combination of operating parameters employed is selected to produce a significant yield of liquid product from a given feedstock, which product is substantially aromatic in nature.
U.S. Pat. No. 3,827,968 discloses an aromatization process wherein the olefin content of a C.sub.2 -C.sub.5 olefin-containing feed is first oligomerized to produce higher molecular weight olefins over a ZSM-5 type zeolite and then contacting the liquid, higher molecular olefins with a zeolite catalyst in a second stage to produce aromatic liquids. The first step of the '968 process differs from the '024 patent in that less severe operating conditions are used to produce a product having a liquid portion consisting principally of C.sub.5 -C.sub.9 olefins. Attempting direct aromatization of certain feedstocks--especially those containing large amounts of paraffins--was apparently found to cause rapid catalyst aging and/or deactivation. Operating conditions employed in the first step of the '968 patent include temperatures of 290.degree.-450.degree. C., pressures up to 800 psig and 0.5-50 hr. .sup.-1 WHSV. The first stage oligomerization effluent, in addition to olefinic liquids, contains a gas product consisting of a highly paraffinic C.sub.4 - stream. In addition, the second stage of the '968 process produces an effluent which may contain up to 50% C.sub.4 - paraffins. The C.sub.4 - paraffin streams are, according to the '968 patent, preferably recycled to a pyrolysis unit.
U.S. Pat. No. 3,960,978 discloses the conversion of gaseous C.sub.2 -C.sub.5 olefins, either alone or in admixture with paraffins, to a gasoline fraction having no more than about 20 wt. % aromatics by contacting the olefin feed with a ZSM-5 type zeolite having a controlled acid activity (i.e., alpha value) of about 0.1-120. Other oligomerization conditions include temperatures of 260.degree.-480.degree. C. (preferably 290.degree.-450.degree. C.), WHSV of 0.1-25 hr..sup.-1 (preferably 0.5-20), and hydrocarbon partial pressures of 0.5 to 40 atmospheres (preferably 0.5-20 atmospheres). An advantage of the process is said to be improved catalyst stability. Example 1 of the patent shows oligomerization of propylene according to the method of the '978 patent. The gaseous product produced was primarily C.sub.4 olefins. The patent suggests recycle of the gaseous C.sub.4 olefin byproduct to extinction.
U.S. Pat. No. 3,972,832 discloses conversion of aliphatic compounds over phosphorus-containing zeolites. Example 8 of the patent shows that when ethylene is contacted with the phosphorus-containing zeolite at 500.degree. C. and a WHSV of about 1.5, ethylene is converted into propylene and C.sub.5 hydrocarbons as the major products. As compared to a zeolite without phosphorus, the olefin/paraffin ratios of the product obtained over the phosphorus-containing zeolite were much higher and the quantity of aromatics produced was much less. Also see U.S. Pat. No. 4,044,065 at column 9, lines 32-48.
U.S. Pat. No. 4,021,502 discloses the conversion of gasesous C.sub.2 -C.sub.5 olefins or mixtures thereof with C.sub.1 -C.sub.5 paraffins to higher molecular weight olefins, over ZSM-4, ZSM-12, ZSM-18, chabazate or zeolite beta. The process is operated under conditions selected to give low yields of aromatics. Temperatures are about 230.degree.-650.degree. C. (preferably 290.degree.-540.degree. C.). WHSV is about 0.2-50 (preferably 1-25). Hydrocarbon partial pressures are about 0.1-50 atmospheres (preferably 0.3-20 atmospheres). An advantage of the process is said to be the stability of the zeolite under the conditions employed.
U.S. Pat. No. 4,070,411 discloses the conversion of lower olefins (e.g., ethylene or propylene) over HZSM-11 catalyst to produce a product having a significant isobutane content. The conversion is effected at temperatures of 300.degree.-500.degree. C. and at space velocities of 0.5-100 WHSV.
U.S. Pat. No. 4,100,218 discloses a process for converting ethane to LPG and gasoline and/or aromatic concentrate by passing olefin effluent from the thermal cracking of ethane over a ZSM-5 type zeolite.
U.S. Pat. No. 4,150,062 discloses the conversion of C.sub.2 -C.sub.4 olefins over ZSM-5 type zeolites in the presence of co-fed water. Temperatures are about 230.degree.-430.degree. C. (preferably 290.degree.-400.degree. C.). Pressures range from atmospheric to 1000 psig (preferably from atmospheric to 450 psig). The WHSV is about 0.2-20 hr. .sup.-1.
U.S. Pat. No. 4,211,640 teaches conversion of olefinic gasoline fractions over ZSM-5 type zeolites to produce gasoline (having enhanced gum stability) and fuel oil.
U.S. Pat. No. 4,227,992 discloses a process for selectively reacting C.sub.3 and higher olefins from a mixture of the same with ethylene to produce products comprising fuel oil and gasoline. Operating conditions are selected such that the C.sub.3 and higher olefins are substantially converted to products comprising fuel oil and gasoline but such that substantially no ethylene will be converted. Generally, operating pressures are within the range of about 100-1000 psig, temperatures are within the range of about 150.degree.-315.degree. C., and space velocities are within the range of about 0.1-10 WHSV (based on the C.sub.3 and higher olefins).
U.S. Pat. No. 4,451,685 teaches conversion of lower olefins to gasoline blending stocks over borosilicate catalysts.
U.S. Pat. No. 4,423,268 teaches oligomerization of normally gaseous olefins over essentially alumina-free molecular sieves (e.g., silicalite).
As noted, conversion of olefins to gasoline and/or distillate products over a ZSM-5 type catalyst is known. See the description of U.S. Pat. Nos. 3,960,978 and 4,021,502, supra. U.S. Pat. No. 4,227,992 discloses operating conditions for selective conversion of C.sub.3 +olefins and no more than 20% ethylene conversion. Closely related is U.S. Pat. No. 4,150,062 which discloses a process of converting olefins to gasoline components. In such processes for oligomerizing olefins using acidic crystalline zeolites, it is known that process conditions may be varied to favor the formation of either gasoline or distillate range products. At moderate temperatures (i.e., 190.degree.- 315.degree. C.) and relatively high pressures (i.e., 42-70 atmospheres) the conversion conditions favor distillate range product having a normal point of at least 165.degree. C. At moderate temperature and relatively lower pressures (i.e., 7-42 atmospheres), the conversion conditions favor gasoline and distillate range products. See U.S. Pat. No. 4,211,640.
One object of the present invention is an improved method for converting ethylene to high yields of heavier hydrocarbons. A more particular object is the production of normally liquid hydrocarbons from ethylene under conditions whereby catalyst productivity is maximized, employing a siliceous crystalline molecular sieve catalyst. Other objects, aspects and the several advantages of the present invention will be apparent to those skilled in the art upon consideration of the following description of this invention and of the appended claims.